Optical mark recognition
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Optical Mark Recognition is a method of computerized input from (usually) paper forms. It is generally distinguished from OCR by the fact that a recognition engine is not required. That is, the marks are constructed in such a way that there is little chance of not reading the marks correctly. This requires the image to have high contrast and an easily-recognizable or irrelevant shape.
One of the most familiar applications of OMR is the #2 pencil bubble exam. Students mark their answers (or other information) by darkening circles marked on a pre-printed sheet. Afterwards the sheet is automatically graded by a scanning machine. Most people know this by the eponym Scantron after the company that is most well known for this.
Other examples of OMR are the MICR recognition of the numbers on the bottom of checks and scannable bar codes.
Recent improvements in OMR have led to various kinds of two dimensional bar codes called matrix codes. For example, UPS now prints a two dimensional bar code on every package. The code is stored in a grid of black-and-white hexagons surrounding a bullseye-shaped finder pattern. These images include error-checking data, allowing for extremely accurate scanning even when the pattern is damaged.
Most of today's OMR applications work from mechanically generated images like bar codes. A smaller but still significant number of applications involve people filling in specialized forms. These forms are optimized for computer scanning, with careful registration in the printing, and careful design so that ambiguity is reduced to the minimum possible. Due to its extremely low error rate, low cost and ease-of-use, OMR is a popular method of tallying votes.